docs: def create_ca_file(anchor_list, filename):
      """
      Concatenate all the certificates (PEM format for the export) in
      'anchor_list' and write the result to file 'filename'. On success
      'filename' is returned, None otherwise.
  
      If you are used to OpenSSL tools, this function builds a CAfile
      that can be used for certificate and CRL check.
  
      Also see create_temporary_ca_file().
      """
      try:
          f = open(filename, "w")
          for a in anchor_list:
              s = a.output(fmt="PEM")
              f.write(s)
          f.close()
      except:
          return None
      return filename